This invention relates to the control of the level of knock or detonation produced in an internal combustion engine.
To obtain the maximum fuel economy and maximum peformance from the engine, it is necessary to run the engine quite close to its knock level. There have been developed engine knock level control apparatus for use in operatiang an internal combustion engine under a light knock condition. One example of conventional apparatus is disclosed and described in U.S. Pat. No. 4,343,278, to Asano, which issued Aug. 10, 1982, and is assigned to the same assignee as is this invention.
Such a conventional engine knock level control apparatus employs a vibration sensor secured to the engine cylinder block to generate a vibration signal corresponding to knock induced vibrations at a characteristic frequency. The vibration signal is applied to a bandpass filter which filters out signal components at frequencies other than the characteristic frequency. The filtered vibration signal is rectified and then averaged in providing a knock limiting level, as indicated by dotted curve C of FIG. 1 which is a graph of engine speed versus vibration level. The apparatus also includes a first comparator which compares the filtered vibration signal with the knock limiting level and generates a knock decision signal when the former exceeds the latter. The knock decision signal is integrated from the time at which an ignition spark event occurs. A second comparator compares the result of integration of the knock decision signal with a reference value which is a variable value depending on the knock limiting level, and generates a timing adjustment signal, thereby retarding the timing of ignition spark events of the engine so as to reduce the engine knock level.
Although apparatus of this kind have many advantages, one difficulty arises in that the engine cannot run sufficiently close to its knock level over the entire range of engine speed, since the knock limiting level C, which increases with increase in engine speed as shown in FIG. 1, should be restricted below another vibration limiting level, indicated by dotted line A, which indicates the vibration level above which heavy vibrations occur to produce the possibility of failure of engine parts such as piston and piston ring.
Furthermore, it is necessary to restrict the level of knock induced vibrations below the level of engine sounds resulting from engine vibrations in order to keep passenger's nerves from being annoyed by knock induced sounds. The engine vibrations which cause engine sounds, are produced mainly when the intake and exhaust valves seat or lift off the associated valve seats. This level of the engine vibrations increases with increase in engine speed, as indicated by curve B of FIG. 1.
Therefore, the present invention provides an improved engine knock level control method and apparatus which can operate an internal combustion engine quite close to its knock level substantially over the entire range of engine operating conditions, thereby maximizing engine peformance and fuel economy.